1. Field of the Invention
The present invention relates to a piezoelectric actuator unit having a piezoelectric vibrator, a manufacturing method thereof, and a piezoelectric structural body to be used to manufacture the piezoelectric actuator unit. The piezoelectric actuator unit, for example, is suitably used as a part of a liquid ejecting head and a micro-pump. Here, the liquid ejecting head ejects liquid drops from a nozzle opening thereof. For example, there are a recording head used for an image recording apparatus such as a printer, a liquid crystal ejecting head used to manufacture a liquid crystal display, and a coloring material ejecting head used to manufacture a color filter available. Further, the micro-pump is a microminiature pump capable of handling a very small amount of liquid.
Further, the present invention relates to a liquid ejecting apparatus for ejecting liquid drops from a nozzle opening thereof. As a typical example of a conventional liquid ejecting apparatus, there is an ink jet recording apparatus having an ink jet recording head for image recording available. As other liquid ejecting apparatuses, for example, an apparatus having a coloring material ejecting head used to manufacture a color filter of a liquid crystal display, an apparatus having an electrode material (conductive paste) ejecting head used for electrode forming of an organic EL display and a face emission display (FED), an apparatus having a biological organic matter ejecting head used to manufacture biological chips, and an apparatus having a sample ejecting head as a precise pipette may be cited.
2. Description of Related Art
As an apparatus using a piezoelectric actuator unit having a piezoelectric vibrator, there is a liquid ejecting apparatus. An ink jet recording apparatus which is a typical example of the same produces a comparatively low noise during printing and can form small dots at high density, so that it has been used recently in many printings including color printing.
The ink jet recording apparatus generally has an ink jet recording head (liquid ejecting head) which is loaded on a carriage and moves back and forth in the width direction (head scanning direction) of a recording medium such as recording paper and a feed means for moving the recording medium in the direction (medium feed direction) perpendicular to the head scanning direction.
In this ink jet recording apparatus, ink drops (liquid drops) are ejected from the recording head to the recording medium in correspondence to print data to print the same. And, the recording head loaded on the carriage is formed so as to eject ink of colors such as black, yellow, cyan, and magenta, thus not only text printing by black ink but also by changing the 4-color-ink ejection rate, full-color printing can be carried out.
FIG. 18 is a sectional view showing an example of the recording head of a conventional ink jet recording apparatus.
A recording head 162 has a case 163 made of synthetic resin and a flow path unit 164 stuck on the front (the left side of the drawing) of the case 163. And, the flow path unit 164 is formed by laminating a nozzle plate 166 having many bored nozzle openings 165, a flow path forming plate 168, an elastic plate 176, and a vibration plate 167.
The case 163 is a block member having a storing space 169 opened on the front and rear thereof. In the storing space 169, a piezoelectric vibrator 161 fixed to a fixing substrate 170 is stored. The piezoelectric vibrator 161 has a longitudinal vibration mode.
The nozzle plate 166 is a thin laminal member that many nozzle openings 165 are bored in line along the sub-scanning direction. The respective nozzle openings 165 are arranged at a predetermined pitch according to the dot forming density. By the vibration plate 167 and the elastic plate 176, an insular thick part 171 with the tip of the piezoelectric vibrator 161 joined and a thin elastic part 172 installed so as to surround the periphery of the thick part 171 are formed. On the flow path forming plate 168, a pressure chamber 173, a common ink chamber 174, and an ink feed port 175 for interconnecting the pressure chamber 173 and the common ink chamber 174 are formed.
And, the nozzle plate 166 is arranged in front of the flow path forming plate 168, and the vibration plate 167 and the elastic plate 176 are arranged on the rear side, and the nozzle and vibration plates 166, 167 and the elastic plate 176 are integrated by adhesion so as to sandwich the flow path forming plate 168 between them, thus the flow path unit 164 is formed.
The tip of the piezoelectric vibrator 161 is joined to the thick part 171 on the rear side and in this state, the piezoelectric vibrator 161 is fixed to the case 163. Further, to the piezoelectric vibrator 161, a flexible cable 177 is connected and via the flexible cable 177, a drive signal (COM) and print data(SI) are supplied.
The piezoelectric vibrator 161 in the longitudinal vibration mode shown in FIG. 18 has a characteristic that when it is charged, it is constricted perpendicularly to the electric field and when it is discharged, it is extended perpendicularly to the electric field. Therefore, in the recording head 162, when the piezoelectric vibrator 161 is charged, it is constricted backward, and the thick part 171 is pulled backward in correspondence with constriction, and the constricted pressure chamber 173 is expanded. In correspondence with the expansion, ink in the common ink chamber 174 flows in the pressure chamber 173 via the ink feed port 175. On the other hand, when the piezoelectric vibrator 161 is discharged, it is extended forward, and the thick part 171 is pressed forward, and the pressure chamber 173 is contracted. In correspondence with this contraction, the ink pressure in the pressure chamber 173 is increased and ink drops are ejected from the nozzle opening 165.
Meanwhile, in the ink jet recording apparatus, to improve the print image quality or to increase the printing speed, it is desirable to reduce the nozzle pitch of the recording head and increase the nozzle density.
However, in the recording head using a conventional piezoelectric actuator unit shown in FIG. 18, to reduce the nozzle pitch and increase the nozzle density higher than the current one is extremely difficult due to the restrictions with respect to manufacturing.
In the recording head, to reduce the nozzle pitch thereof is to simultaneously reduce the pitch of the pressure chambers and when the pitch of the pressure chambers is reduced like this, the gap between the insular thick part formed above the pressure chambers and the partitions of the pressure chambers are narrowed. This results in causing an increase in the reaction force when the piezoelectric vibrator is driven and making the cross talk during printing worse and peeling-off of the member forming the recording head.
As mentioned above, there is a limit to improvement of the nozzle density (reduction in the nozzle pitch), so that there is a method of increasing the number of nozzle rows instead of increasing the number of nozzles in one row, thereby increasing the total number of nozzle openings formed in one recording head.
However, in the constitution of a conventional recording head, the number of piezoelectric actuator units must be increased according to an increase in the number of nozzle rows. Generally, one piezoelectric actuator unit is manufactured from one laminate bulk composed of laminated piezoelectric material layers and electrode layers. Therefore, laminate bulks as many as the number of piezoelectric actuator units to be manufactured is necessary, thus the manufacturing cost is inevitably increased. Further, generally, when assembling a recording head, it must be wired (tape carrier package, etc.) for each piezoelectric actuator unit, so that the number of necessary wires is increased in correspondence with an increase in the number of piezoelectric actuator units, thus the manufacturing process is complicated and the neighborhood of the recording head is complicated.
Further, an art for forming two piezoelectric vibrator rows from one laminate bulk is proposed (Japanese Patent Laid-Open Publication No. 8-11304). However, the art forms a slit in the center of the laminate bulk to isolate the piezoelectric vibrator rows, so that for example, regarding laying of wires, after all, similarly to the constitution of installing two separate piezoelectric actuator units, the wiring is inevitably complicated.